RFC: backporting GEOM to the 4.x branch

[ALeine]

dillon at xxxxxxxxxxxxxxxxxxxx wrote: 

>     Sure, but I have a wish list a mile long and probably a thousand man-hours
>     worth of work in my queue.  I'm not going to be porting that any time 
>     soon.  You are certainly welcome to port it as a char device. Our 
>     disk abstraction is already fully recursive so it should be possible to
>     stack any number of block devices on top of each other.  It would be nice
>     to have a common utility to glue block devices together for this class
>     of 'virtual' block device as well.

I know you have other more important priorities, I did not expect you to port
it instead of me. :-) Is someone already working on such a utility?

>     The current BUF/BIO model is very close to FreeBSD-4.  We haven't done any
>     of the truely major bits of work on it yet (like changing the block
>     numbers to 64 bit byte offsets and things of that ilk).

What other major changes that would affect what I would like to implement are
planned? Anything else I should anticipate?

>     The only big difference relative to FreeBSD-4 is that the actual I/O
>     sequencing has changed slightly, and the device representing a labeled
>     disk is no longer overloaded onto the device reprsenting a 'raw' disk.

That would indeed make it easier to implement dGDE, I'll take a closer look
and study the code.

ALeine
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